1. Field of the Invention
This invention relates to spring-applied parking brakes for transit vehicles which normally are released by use of pneumatic pressure. It further involves the manual release and reapplication of the brake, for example, when pneumatic pressure is not available.
2. Description of Related Art
Service brakes for transit vehicles are normally applied by pneumatic cylinders supplied with the pressurized air by the lead vehicle or engine. When vehicles are separated from the lead vehicle, parking brakes are desirable to prevent runaway motion. Typically, the parking brakes are spring applied. Pushrods connected to spring actuated pistons connect with linkages effecting service braking. The spring-applied brakes can be released by pneumatic pressure once the vehicle is reconnected to a lead vehicle or source of air pressure. In some prior art spring-applied brakes, a manual release is provided for disconnecting the piston from the pushrod, thus permitting movement of the vehicle. This spring-applied brake cannot be reactivated until pneumatic pressure is again available. See U.S. Pat. No. 5,848,550 entitled “Parking Brake Manual Release Mechanism.” The brake disclosed therein includes a collet connection between the piston and pushrod for effecting slack adjustment in the service brake mode. In other prior art, the application and release of the parking brake force is effected with either air pressure or with a mechanical winding action. In this case, the connection between the spring driven piston and the pushrod is controlled by a nut threaded on the pushrod, the rotation of which is secured by a pneumatically controlled clutch. During parking brake application, the nut is prevented from rotating with a toothed clutch which is released when air pressure is reapplied to reset the brake unit.